Typical gas-fired domestic and light commercial water heaters comprise a tank in which water is heated and stored. The burner is controlled by a thermostat that strives to maintain a set temperature for the water. Examples of energy conservation measures that have been adopted by the manufacturers of these appliances in order to improve their efficiency include better thermal insulation of the tank and electronic ignition for the burner. In the United States there has been little fundamental change however in the basic concept of such a water heater: it still comprises a tank in which heated water is stored ready for use.
An on-demand gas-fired water heater would be a distinct improvement from the standpoint of energy conservation because it would have no such reservoir from which heat is wastefully dissipated to the surroundings. But an essential requirement for a commercially viable appliance of this type is that it be manufacturable at a price that is reasonably competitive in the marketplace, taking into account its improved efficiency. A further requirement is that it not occupy any significantly larger amount of space than do present commercial water heaters of equivalent hot water delivery ratings, and preferably that it occupy less space.
A preliminary novelty search conducted in connection with the present invention developed U.S. Pat. Nos. 4,909,191; 1,582,230; 4,453,496; 4,867,106; 4,401,058; 4,366,778; 4,096,616; 4,825,813; and 2,537,984.
U.S. Pat. Nos. 4,453,496 and 4,825,813 describe what are designated "once-through type boilers". Such a boiler comprises an upright cylindrical enclosure whose interior contains a heat exchanger in the form of an annular lower manifold, an annular upper manifold, and a number of tubes arranged in a circular pattern and extending between the two manifolds. Cold water is introduced into one of the manifolds, passes through the tubes to the other manifold, and is discharged from the latter manifold. A gas burner is disposed within the center of the lower manifold and the hot products of combustion pass over the exteriors of the tubes, heating the water in the process. In order to improve the efficiency of the heat exchanger, fins are disposed on the exteriors of the tubes.
The general concept of mounting fins on a tube by stacking individual fin elements on the outside of a tube is not novel. The concept is shown by U.S. Pat. No. 2,537,984.
U.S. Pat. No. 4,909,191 discloses a hot water appliance having a heat exchanger that is in certain respects similar to those of U.S. Pat. Nos. 4,453,496 and 4,825,813. Each of its tubes that extends between its manifolds is actually a "tube-within-a tube", one of which carries "sanitary" water and the other of which carries "radiator" water. The side of the heat exchanger is enclosed by a cylindrical wall that is spaced inwardly from the casing's side wall to define an annular cylindrical space surrounding the heat exchanger. Combustion air flows through this space before reaching the gas burner, which interestingly is disposed within the center of the upper manifold.
U.S. Pat. Nos. 1,582,230; 4,401,058; and 4,366,778 show other forms of water heaters having similar heat exchangers.
U.S. Pat. No. 4,096,616 discloses a heat exchanger comprising concentric tubes with inserted fins, and U.S. Pat. No. 4,867,106 discloses a hot water heater in which the combustion gases flow flow through a helical path that is formed by a helical insert disposed within a tube.
The present invention relates to a new and unique on-demand gas-fired water heater and heat exchanger which exhibit ultra-high efficiency in a relatively compact volume and which can be manufactured using known technology to be competitively priced with available appliances, taking into account the energy savings that are obtainable with the present invention due to its improved energy efficiency. Appliances embodying principles of the present invention are well-suited for mass-production fabrication in various model sizes.
The distinguishing features of the present invention and its many attributes will be seen in the ensuing detailed description of a presently preferred embodiment that represents the best mode contemplated at the present time in carrying out the invention. Drawings accompany the disclosure and are briefly described as follows.